Thermal responsive control device



Aug. 24, 1954 Filed April 14, 1950 L. J. KOCI THERMAL RESPONSIVE CONTROLDEVICE a Shefcs-Sheet 1 INVENTOR.

Aug. 24,, 1954 L. J. KOCI 2,687,469

THERMAL RESPONSIVE CONTROL DEVICE Filed April 14, 1950 3 Sheets-Sheet 2hm. Nu

mmvrox. I (f 12 001 Aug. 24, 1954 L. J. KOCI 2,687,469 THERMALRESPONSIVE CONTROL DEVICE Filed April 14, 1950 3 Sheets-Sheet 3 at alower serving temperature.

Patented Aug. 24, 1954 UNITED STATES PATENT OFFICE 2,687,469 THERMALRESPONSIVE CONTROL DEVICE Ludvik J. Koci, Brookfield, 111., assignor tosum beam Corporation, Chicago, 111., a corporation of IllinoisApplication April 14, 1950, Serial No. 155,981 '13 Claims. (Cl. 21943)lower heating chamber While the coffee grounds are placed in the upperchamber. As the Water is heated in the lower chamber, water vaporpressure is created above the liquid in this chamber which, when thetemperature approaches the boiling point or" water, forces the waterfrom the lower chamber into the upper chamber to infuse the cofieegrounds contained therein. When the heat is removed from the lowerchamber, it cools so that the water vapor contained therein condenses tocreate a vacuum thereby causing coffee to pass from the upper chamberthrough a suitable filter into the lower chamber where it preferably ismaintained at a desirable serving temperature which could be of theorder of 180 F.

During the coffee making operation, the water is initially heated towellover 200 F. After the cofiee has been made, however, it is desirable tomaintain its temperature at around 180 F., which is considered to be adesirable serving temperature, which serving temperature may be higheror lower, depending upon the taste of the individuals concerned. In someof the early automatic coffee makers, it was common practice to providetwo heating elements, one for producing the high heat required duringthe coffee making operation, and the other to maintain the cofieeInitially, individual control means for each heating element wereprovided. More recently it was suggested to use a heating element withtwo independent control devices to control the two temperature rangesthereof. Such an arrangement is disclosed in copending Jepsonapplication, Serial No."794,959, filed December 31, 19 %7, now U. S.Patent 2,664,811 granted January 5, 1954 and assignedto the sameassignee as the present application. One control device in thiscopending application is adaptedto control the coffee maker temperaturefor serving. The

during the coffee making operation and particularly during the high heatinterval. Subsequently a second control device in the form of a thermalresponsive element takes over the con- 2,312,555 referred to above,there is disclosed and claimed an arrangement whereby a single heatingelement and a single thermal the desired present invention is concernedwith an improvement on the thermal control device of the above mentionedJ epson patent, still employing a single heating element of an improvedtype and a single thermal responsive device, which is simple andcompact, may be manufactured as a sub-assembly, and which is fool-proofin operation.

In cooking devices and other heating apparatus, it is sometimesunnecessary to provide a control of the type disclosed above where asingle thermostat and a single heating element control energization ofthe heating element in two temperature ranges. The improved thermalresponsive device of the present invention is equally Well suited foruse in other cooking devices or heating apparatus, even where the twotemperature range feature discussed above is not desirable, and anapplication of the present invencan economically be employed inapplications such as those just mentioned, while still being useable inapplications where control in two temperature ranges is required.

In prior control devices it has been customary to require a substantialforce to be moved even .mal responsive device shown in the with theinitial deflection of a thermal responsive element. This sometimesresulted in improper operation, and it would be desirable to provide athermal responsive control of snap acting type and so arranged as to beindependent of the effect of frictional resistance, contact welding,etc.

Accordingly, it is an object of the present invention to provide a newand improved thermal responsive control device particularly well adaptedfor use with automatically controlled electric cooking devices andheating apparatus.

It is another object of the present invention to provide an improvedthermal responsive control device particularly well adapted for use withvacuum type coffee makers whereby a single heating element and a singlethermally controlled switch produce a high brewing heat, and thereaftermaintain the device at a lower heat to keep the coffee produced in asuitable condition for serving.

It is a further object of the present invention to provide an improvedautomatic coffee maker having an unusually simple and compact automaticheating control capable of performing the functions required of such acoffee maker.

Still another object of the present invention is to provide an improvedsub-assembly of a thermal responsive device adapted for readyassociation with a coffee maker of the automatic type or similar cookingapparatus to provide control in two temperature ranges with a singleheating element and a single thermal responsive switch.

A still further object of the present invention is to provide a thermalresponsive control device for an automatic coffee maker or other cookingdevice which is simple and sturdy in construction, economical tomanufacture and which is capable of giving years of satisfactory andfoolproof service.

Further objects and advantages of the present invention will becomeapparent as the following description proceeds and the features ofnovelty which characterize the invention will be pointed out withparticularity in the claims annexed to and forming a part of thisspecification.

For a better understanding of the present invention, reference may behad to the accompanying drawings in which Fig. 1 is a perspective viewof an automatic coffee maker representative of a cooking device withwhich the present invention is particularly applicable;

Fig. 2 is a reduced sectional view taken on line 2-2 of Fig. 3, assumingFig. 3 shows the complete structure;

Fig. 3 is an enlarged sectional view taken on line 3-3 of Fig. 2assuming that Fig. 2 shows the complete structure;

Fig. 4 is a sectional view taken on line d& of Fig. 3, assuming thatFig. 3 shows the complete structure;

Fig. 5 is an enlarged fragmentary view of a portion of the coffee makerof Fig. 1;

Fig. 6 is a somewhat schematic diagram illustrating the electricalconnections of a cooking device embodying the present invention with theelectric heating element shown in its energized condition;

Fig. '7 is a somewhat schematic view of the thermal responsive device ofthe present invention shown in the high heat position thereof; and

Fig. 8 is a view similar to Fig. '7 with the thern w h t positionthereof.

Basically, the present invention is concerned with a control device inthe form of a sub-assembly comprising a supporting plate having mountedthereon a bimetallic element, which has one end thereof fastened to saidplate. The free end of the bimetallic element is connected to a somewhatresilient like member pivotally supported so that the bimetallic elementhas two more or less stable positions and moves with a snap actionbetween these two positions. In either of these two positions, thebimetallic element is capable of deflecting and performing a controloperation, thereby providing automatic control in two differenttemperature ranges. A suitable switch associated with the bimetallicelement is capable of being opened and closed in the extreme positionsof the bimetallic element. A manual lever is provided automatically tomove the bimetal to what might be termed its high which has a somewhatsetting. When a sufficiently high temperature is reached, the bimetallicelement snaps over into its other position, which may be termed its lowposition, and it is in this low control position that operation tomaintain constant a certain desired lower temperature is provided.Simple means are included whereby the temperature at which thebimetallic element moves from its high position and also the temperatureat which the cooking device is maintained at the low setting, areindependently adjustable. By appropriately adjusting the latter, thedevice may operate solely to open and close a circuit without any lowtemperature control.

Although the present invention is applicable L to control heatingdevices in general, it is particularly well adapted to control cookingdevices such as automatic coffee makers. Sclely for the purpose ofdisclosing the present invention, it has been illustrated as applied toa coffee maker. Referring now to the drawings, there is illustrated inFig. 1 an automatic coffee maker generally designated at it comprising alower water heating chamber or vessel l i and an upper coffee infusionvessel or chamber !2. These vessels may be formed of any suitablematerial such as glass, metal or the like. Preferably, however, thevessels are formed of a suitable metal such as a chromium plated copperor the like and each vessel is provided with a suitable handledesignated at E3 and M for the Vessels if and i2 respectively. The lowervessel M which is commonly designated as the pot, since it may be usedas such, following the removal of the upper vessel at the completion ofthe coffee making operation, supports the upper vessel 92 in the mannerindicated during the coffee making operation. The vessel i2 is adaptedto be closed by a suitable cover l5 which may be used with the pot Hwhen the latter is used as a conventional coffee pot after the coffeemaking cycle has been completed.

As in the Jepson Patent 2,312,555 referred to above, the lower vessel orpot ii is provided with a bottom ll, best shown in Fig. 3 of thedrawings, conical configuration so as to provide a low point at thecenter of the pot. For the purpose of heating liquid disposed within thelower vessel if, there is provided a heating element it which is in goodheat exchange relationship with the under or nonliquid engaging side ofthe bottom ll or, in other words, with the side which is effectivelyoutside the pot H. As illustrated, the heating element 118 is preferablyof the well known sheathed form comprising an outer metal sheath 19within which is disposed a resistance element 29 preferably disposed inthe form of a spiral-coil and spaced and supported electricalinsulatsingle turn of sheathed heating element Hl-need be employedand toinsure uniform heating, the bottom ll of the vessel I l is preferablyformedofa material having a very highheatconductiv ity. Sheet copper hasbeen found to be especially satisfactory and preferably the heatingelement I8: is brazed to the sheet copper bottom ll, as indicatedat 22inFig. 3 of' the drawings. conductivity of such sheet copper has beenfound sufliciently good so that fairly uniform heating occurs throughoutthe entire surface of the bottom i1, even though the heating element 58is brazed to a relatively small area thereof.

As in the above mentioned J epson patent, there is-provided centrally ofthe'bottom ll of the pet I I, asupporting stud 24 which extends belowthe bottom I! for supporting various portions of the control device ofthe present invention described in greater detail hereinafter. Asillustrated, the bottom ll of the vessel II. is provided at its lowcentral point with an opening defined at 25 for receiving a hollow rod26 of copper or the like, which has an annular flange adapted to bepeened over as indicated at Zl'so as to embrace the edges of the opening25 in a manner clearly indicated in Fig. 3 of the drawings. The stud 24has its head Zea seated in a recess defined at one end of the hollow rod26. Preferably, the bottom ll, the hollow rod 26 and the stud 24 areintimately united as by brazing orthe'like to form a leak proof vessel Hand to rigidly support the stud 24'from the vessel I l in the mannerindicated.

In order to define a control chamber for the automaticallycontrolledcooking device or heating apparatus Hi, there is'provided a somewhatbowl shaped base 35 preferably formed from a molded insulatingassocia'tedwith the vessel H, a pleasing exterior appearance isprovided, Fig. l of the drawings. This base has integrally formedtherewith, suitable legs 3! for supporting the pot to provide The bottomside of the base is provided with a relatively large central opening 32adapted to be closed by a suitable closure plate as which abuts againstan annular shoulder 34 definedaronnd the opening 32. Preferably, thecenter of: the closure plate 33 is provided with an indentation defininga recess 36 toaccomniodate a nut 37 threadedly engaged with the stud zi'so as not only to hold the closure plate 33 in position, but also tomaintain the base'39'in assembled rela tionship with the vessel H, thusdefining the control chamber 49 for accommodating the control mechanismof the cooking device. to be. described'hereinafter. The closure plate33 may be provided, if desired, with therein to accommodateascrewdriver'or other toolwhen making the necessary adjustments of thethermal-responsive control device described hereinafter, and theseopenings may then be closed bya suitable decorative: plate i i: heldinThe.

plastic and shaped so that when as clearly indicated in ventilationbelow the same.

suitable openings H place :by a: screwr42: threaded into the lowermostend ofthe'stud'24;

The moldedbase 30 preferably also includes integral wall portionsdefining a'recess 43-wherein are disposed the contact pins 44 and 45which may. be suitably connected to a conventional appliance cord, thecontact pins and 45 providing bayonet type contacts. The recess 43' isdesigned to receive the conventional female type plug contact which ispreferably connected by means of the conventional appliance cord, notshown, to any suitableelectrical outlet. shown in 2 ofthe drawings, thecontact pins trol arrangement, to be described'in detail hereinafter,disposed within the base 3-9. Additionally the. base 3d'is providedwithan opening or slot' ll through which a suitable vertically movable,manually actuable member 49- may extend for manual actuation of thecontrol mechanism. When the present invention is employed to control adevice such as the egg cooker disclosed and claimed in copending Jepsonapplication, Serial No. 155,977, filed April 14; 1950, appropriate onand ofi indicia will-be'provided upon the base 39 adjacent the opening4?. Where the cooking device is. such as to require control in twotemperature ranges, appropriate indicia indicating the high or lowsetting of the device is provided. Asbest shown in Fig. 5 of'thedrawings, the base 3th. is providedwith'a raised-surface 48 adjacent theopening Mon which appropriate indicia such as low and high setting ofthe manually actuable member 49 disposed in the opening 47;

The vessel it includes one additional element notdescribed heretofore,comprising the stud or pin suitably welded or integrally formed with thebottom ll, anddisposed adjacent the periphcry of the vessel l l and moreor less mid-way between the ends or terminals ltd-and 13b of the heatingelement l3.

In accordance with the present invention, the controlmechanism forcontrolling the supply of electrical energy to the electric heatingelement [8 comprises a sub-assembly which is supported from the stud 24and may readily be assembled or removed from stud 24 as a unit. Asillustrated, this sub-assembly comprises a main supporting plate 52having turned up edge flanges 52c along the sides thereof to provideincreased rigidity. As illustrated, in Fig. 2 of the drawings the mainsupporting plate 52 has a configuration somewhat of the shape of thetail of an arrow, although it will be understood that the particularshape employed is immaterial. The supporting plate 52 is provided with.a central opening 5- through which the stud 24 may extend when cookingvessel with which'it is associated. As illustrated in the drawings, theplate 52 is adapted to have one side thereof engage the copper rod 26whereupon suitable nuts 54' and Edmay be applied'to the stud 24 asindicated in Fig. 3 of the drawings to maintain the plate in properassembled relationship. Preferably, the plate 52 is provided at one endwith a pair of legs 52b comprising an integral part of the plate whichengage the bottom I! of the vessel H to provide spaced supports for thisend of I the plate 52.

For the 'purposeofproviding temperature conis providedto indicate thethe plate is assembled with thetrol, the sub-assembly includes abimetallic element 55 which has one end thereof attached to the end ofplate 52 remote from the legs 52b as by means of a spacing rivet B. Thespacing rivet 55 provides such a spacing that at normal temperatureswhen the plate 52 is assembled to the stud 24, a substantial portion ofthe bimetallic element 55 lies against and in intimate heat exchangerelationship with the bottom II. This provides a marked advantage overprior art devices where it was customary to transfer heat to thebimetallic element through a suitable contact stud or the like with theinherent problem of having poor heat transfer, where the stud was weldedor brazed to the heated device. By having the bimetal 55 inherentlybiased against the bottom i1, good heat transfer with the very surfacewhich it is desired to control, is assured.

With the arrangement described thus far, the sub-assembly comprising themain supporting plate 52 is held in place by a single central fasteningmeans and there is some danger of movement or rotation of the plate 52about the axis of the stud 24. To prevent this, the bimetal 55 has aportion 55a extending slightly beyond the rivet 55 which portionincludes a notch 55?: for receiving therein the stud 55 welded orotherwise secured to the bottom I? of the vessel M. It will be apparentat once that this firmly secures the sub-assembly comprising the mainplate 52 in position since it positively eliminates any rotation thereofabout the axis of the stud 24. The high expansion side of the bimetal 55is in contact with the perature conditions so that upon heating of thebottom H, the bimetal 55 tends to have its free end move away from thebottom ii.

In order that the bimetal 55 may operate with a snap action to performthe control functions described in detail hereinafter, the free end ofthe bimetal is connected as by suitable rivets. or other fastening meanssuch as 58, with an extension 59a of resilient spring member 59illustrated in the shape of a flat disk of oval configuration. Theextension 55a is on one side of the oval and a similar extension 5% isprovided on the other side of the oval which is connected to the one endof a suitable lever 58 by suitable means such as rivets 5|. The 1ever 65at an intermediate point thereof is pivotally mounted to an L-shapedsupport 52 suitably secured as indicated at 53 to the supporting plate52. The pivotal support of the lever 55 is accomplished by virtue of anopening 55a defined in this lever which engages with a hookshapedextension 62a of the pivotal support 52. The pivotal support 62furthermore may be adjusted by virtue of an adjusting screw 65 so as tocontrol the compressive force applied across the ends of the snap actingassembly comprising the bimetal 55, the resilient member 59 and theportion of lever 55 between the resilient member 59 and the pivotalsupport 52'. It will be noted from an examination of Fig. 3 of thedrawings that the L-shaped support 52 is formed of resilient materialand by virtue of the compressive force of the snap acting assembly tendsto have the leg thereof fastened by the rivet 63 moved away from thesupport 52 in dependence upon the adjustment of the screw 54. As thescrew 54 clamps the riveted leg of the pivotal support 62 closer againstthe support 52, the compressive force applied to the snap actingassembly is increased. It should be understood bottom i1 under lowtemthat although the resilient member 59 is described as an oval disk,actually it may have any suitable configuration. The reason a somewhatoval shaped disk member is employed, is two fold. First, it was found togive the desired longitudinal softness to the snap acting assembly toprovide a substantial range of movement of the snap acting device.Secondly, such an oval member readily accommodates the supporting stud 2which, as may be noted, is disposed within the oval.

As the compressive force applied across the snap acting assembly isdecreased suificiently, the bimetal will tend to remain against thebottom 11 of the vessel H, and if it is moved to a position away fromthe bottom, it will always tend to snap back against the bottom while atroom temperature. On the other hand, when a sufilcient compressive forceis applied across the ends of the snap acting assembly including thebimetal and the resilient member 55, a large range of snap actingmovement is obtained and the bimetallic element will assume two stablepositions, one as shown in Fig. 7 and one as shown in Fig. 8 of thedrawings. Movement from the Fig. '7 to the Fig. 3 position is occasionedthrough heating of the bimetal 55, while movement in the other directionrequires manual actuation. In order to accomplish such manual resetting,the lever 60 is provided with an extension 651) which extends throughthe opening 4'! described above and has attached thereto the manualactuating knob 59. Preferably the extension 60b is provided with adeformed portion such as Bile which permits ready assembly with knob 49but prevents disassembly.

By properly adjusting the pivotal support 62 through manipulation of theadjusting screw 64, the temperature at which the bimetal 55 moves fromthe position shown in Fig. '7 to the position shown in Fig. 8 mayproperly be adjusted. For use with a cofiee maker, it is desirable thatthis temperature be somewhat above 200 F. such as, for example, 240 F.to insure that all the liquid has moved to the upper vessel l2. Whenthis has occurred it is only desirable to control the heating element [8to maintain the coffee at the proper temperature for serving.

In order to control the electrical circuit including the heating element18, there is supported on the sub-assembly including the plate 52, anelectrical switch comprising a'stationary contact 55 suitably attachedto a stationary contact arm 55 which is supported in insulatedrelationship by insulating means 61, 63 and 65 from the support 52 as bya rivet l0 and clamping plate 15a. The switch further includes a movablecontact H supported on a resilient contact arm l2 which is illustratedas having an L-shaped configuration as best shown in Fig. 2 of thedrawings. The end of the contact arm 12 supporting the contact H is freeto move, whereas the other end is fastened as by a rivet 13, tosupporting plate 52 but is insulated therefrom by suitable insulatingmeans i4, i5 and 16. The relative movement between the contacts 65 and His produced through bending of the resilient contact arm 12.

Movement of contact arm 12 is produced in response to deflection of thebimetal 55 by virtue of an insulating extension 25 adjustably supportedfrom the resilient arm 12 as best indicated in Fig. 4 of the drawings.This insulating member i9 is disposed in the path of movement of themoveable end of the thermal responsive element 55 so as to be struckduring the snap acting movenal l8b of the heating element it.

moved to the position shown in Fig. 8 of the drawings, the extension "i9is preferably adjustably supported on the arm 72 as by a threadedadjusting screw 80 threadedly mounted in a nut 8| suitably supported onthe arm 12.

.understood that it is desirable for the arm 72 to be relatively rigidin its intermediate portion to insure uniform operation and to thisextent the resilient arm i2 is preferably provided with side flanges 32aadjacent its intermediate portion. It will be understood also that ifdesired, the stop member 19 may be non-adjustable and instead, .thecontact H or the contact 65 may be adjustable to perform the samefunction. Thus, it will be apparent that adjustment of the operatingtemperature in the high range of operation is controlled by theadjusting screw 6% while adjustment of the temperature to be maintainedin the low range is controlled by the adjusting screw 80.

For the purpose of completing the electrical circuit through the switchcomprising the contacts 65 and ll and the heating element It thestationary contact arm 56 is electrically connected by means of aconductor 85 directly to the termi- The other terminal of the heatingelement is i connected by means of a conductor 85, which be a fiatribbon conductor, with the terminal pin The other terminal pin M. isconnected means of a ribbon conductor 51 with the resilient contact arm12 which latter may be provided with suitable terminal mean tofacilitate the ready interconnection. The electrical circuit can readilybe ascertained from an examination of Fig. 6 of the drawings where theelements are schematically indicated and are designated by the samereference numerals as in the structural views of the device.

In view of the detailed description included above, the operation of thecontrol device of the present invention will readily be understood bythose skilled in the art. irst of all, the entire control device is inthe form of a subassembly mounted on a supporting plate 52 which isatthe cooking device in a simple manner. When the device of the presentinvention is used to control two temperatures, such as the brewingtemperature of an automatic coffee maker, and

subsequently a low serving temperature, the

manual control button 59 is moved to the high position as shown in Fig.3 of the drawings when it is desired to initiate the coffee makingopera- This, of course, insures closure of the switch at the contact 55and ii. By appropriate adjustment of the ad-usting screw (it, thecontacts will remain closed until a relatively high temperature isreached, such as a temperature of the order of 240 F. All this time thebimetal 55 Will have been heated to such an extent that deflectionoccurs and when a sufficien force has developed, the bimetal will snapover from the position shown in Fig. 7 or" the drawings, to the positionshown in Fig. 8, whereupon control in the low temperature range willresult. Since the bimetal 55 is at an elevated temperature immediatelyfollowing snap acting movement from the high to the low setting, thecontacts Edand 7! will remain separated until suincient cooling of thevessel I I occurs to drop the temperature to that for'which theadjusting screw 89 has been set and, thereafter, the bimetallic element55 will 49 is restored to the high setting. This construction provides avery satisfactory arrangement in that no force for causing opening ofthe contacts is encountered'by the bimetallic element 55 until it moveswith a snap action whereby it has sufiicient force to openthe contacts.In prior art arrangements, even the initial movement of the bimetallicelement was opposed by the friction of the contacts to be operated andthe frictionof associated parts, and this high friction oftentimescaused unsatisfactory operation.

In the event that the control device of the present invention is usedonly in one range, such as the high temperature range, the adjustment ofthe stop 79 is such that under normal conditions, the bimetallic element55 will never be cooled sufficiently to permit reclosing of the circuitat the contacts s5 and ill, unless the bimetallic element is moved backto its initial position. This means, of course, that the adjusting screwas is so adjusted that for any deflection of the bimetallic element 55,while in the Fig. 8 position of the drawings, the contacts t5 and Hremain separated.

While there has been shown and described certain particular embodimentsof the present invention, it will be understood that various changes andmodifications of the invention will occur to those skilled in the art.It is aimed in the appended claims to cover all such changes andmodifications as fall wit in the true spirit and scope of the presentinvention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. Thermal control means for a cooking device and thermal responsiveswitch means for controlling the rlow of current to said heating unit,said thermal responsive switch means including including a resilientelement incorporated in a snap acting over center mechanism whereby saidresilient element assumes two relatively spaced positions, meansresponsive to a predetermined bimetallic element for alternately openingand closing the circuit controlled by said switch means while saidresilient element is in said one of said-two positions to maintainconstant the temperature of said cooking device at a temperature belowsaid predetermined high temperature.

2. In a cooking device of the type including an electric heating unitand a pair of relatively movable contacts for controlling the flow ofcurrent to said heating unit, thermal control means comprising asub-assembly including a supporting plate'for said contacts, abimetallic element having one end thereof supported on said plate,resilient means pivotally mounted on said plate and connected to theother end of said bimetallic element to provide a snap acting overcenter mechanism whereby the other end of said element may assume tworelatively widely spaced stable positions, means responsive to movementof said bimetallic element to said one of said positions in response tothe attainment of a predetermined temperature of said cooking device forproducing relative separation of said contacts, manual means for movingsaid element to the other of said positions to close said contacts andmeans for supporting said plate from said cooking device with saidbimetallic element in direct intimate heat exchange relationship withsaid cooking device over a substantial length of the movable portion ofsaid bimetallic element when in one of said two spaced positionsthereof.

3. Thermal control means for a cooking device of the type including anelectric heating unit and a pair of relatively movable contacts forcontrolling the flow of current to said heating unit, said thermalcontrol means comprising a bimetallic element having one end thereofsupported from said cooking device, resilient means connected to theother end of said bimetallic element and pivotally mounted in spacedrelation to said other end of said element for maintaining said elementunder compression to provide a snap acting over central mechanismwhereby said other end of said element may assume two relatively widelyspaced stable positions one of said positions being in direct maximumintimate heat exchange relationship with said device and the other beingin less intimate heat exchange relationship with said device, meansresponsive to movement of said bimetallic element to the other of saidpositions in response to the attainment of a predetermined hightemperature of said cooking device for producing relative separation ofsaid contacts, means connected to said pivotally mounted means formanually returning said element to said one position, and meansincluding said element for alternately opening and closing Said contactswhile said element is in said other of said positions to maintainconstant the temperature of said cooking device at a temperature belowsaid predetermined high temperature.

4. A thermal control means for a cooking device of the type including anelectric heater and a pair of relatively trolling the flow of current tosaid heater, said thermal control means comprising a sub-assemblyincluding a supporting plate for said contacts, a bimetallic elementhaving one end thereof supported on said plate, a closed loop of flatresilient material having one edge pivotally mounted on said plate andthe other edge connected to the other end of said element, means forapplying a longitudinal compressive stress to said element and acrosssaid loop to provide a snap acting over center mechanism whereby theother end of said element may assume two relatively widely spaced stablepositions, means responsive to movement of said bimetallic element toone of said positions for producing relative separation of saidcontacts, and means for mounting said supporting plate from said cookingdevice with said bimetallic element in intimate heat exchangerelationship therewith when in at least one of said two widely spacedpositions thereof.

5. A thermal control means for a cooking device of the type including anelectric heater and a pair of relatively movable contacts forcontrolling the flow of current to said heater, said movable contactsfor conthermal control means comprisin a sub-assembly including asupporting plate for said contacts, a bimetallic element having one endthereof supported on said plate, means pivotally mounted on said plateand connected to the other end of said bimetallic element comprising aclosed loop of flat resilient material, means for applying alongitudinal compressive stress to said element to provide a snap actingover center mechanism whereby the other end of said element may assumetwo relatively widely spaced stable positions, said compressive stressbeing applied across diametrically opposed points on said loop whichprovides longitudinal softness to said over center mechanism, meansresponsive to movement of said bimetallic element to one of saidpositions for producing relative separation of said contacts, and meansfor mounting said supporting plate from said COOkll'lg device with saidbimetallic element in intimate heat exchange relationship therewith whenin said one of said two widely spaced positions thereof.

6. For use with a cooking device of the type including an electricheater and a pair of relatively movable contacts for controlling theflow of current to said heater, a thermal control means comprising, asub-assembly including a supporting plate for said contacts, abimetallic element having one end thereof supported on said plate, meansincluding a closed loop of fiat resilient material for pivotallyrelating the other end of said element to said plate, means for applyinga compressive force longitudinally of said element to provide a snapacting over center mechanism whereby the other end of said element mayassume two relatively widely spaced stable positions, means responsiveto movement of said bimetallic element to one of said positions forproducing relative separation of said contacts, means for mounting saidsupporting plate on said cooking device with said bimetallic element inintimate heat exchange relationship therewith when in the other of saidtwo widely spaced positions thereof whereby said element moves to saidone position in response to a predetermined high temperature of saiddevice, and means for controlling said contacts when said element is insaid one of said positions to maintain said cooking device at arelatively constant temperature below said predetermined hightemperature.

'7. A temperature control arrangement for an electric heating devicecomprising a thermostat bar having one end fixed and its other endmovable in response to changes in temperature, a resilient memberfastened to the movable end of said bar, means for applying acompressive force longitudinally of said bar and across said resilientmember to cause said bar to move quickly from a first position to asecond position, means for adjusting said compressive force to vary thetemperature at which said bar moves from said first position to saidsecond position, switch means capable of being actuated in response tosaid quick movement of said bar from said first position, and meansincluding said element for alternately opening and closing said switchmeans while said bar is in said second position to maintain thetemperature produced by said heating device at a constant value belowthe temperature at which said bar moves from said first position.

8. A temperature control arrangement for an electric heating devicecomprising a thermostat bar having one end fixed and its other endmovend of said bar, means for applying a compressive forcelongitudinally of said bar and across said resilient member to causesaid bar to move quickly from a first position to a second posi tion,means for adjusting said compressive force to vary the temperature atwhich said bar moves from said first position to said second position,normally closed switch means for controlling the flow of current to saidheating device. means actuable upon a predetermined free quick mov mentof said bar from said first position to cause opening of said switchmeans, and means for a"- the operation of said last mentioned meanswhereby said bar while in second po sition controls said switch means tomaintain the temperature produced by said heating device at a levelbelow the temperature at which said bar moves from said first position.

9. Thermal control means for a cooking devic of the type including anelectric heating unit and thermal responsive switch means forcontrolling the flow of current to said heating unit, said switch meansincluding a bimetallic element havone end thereof supported from saidcooking device, resilient means engaging the free end of said elementfor applying a longitudinal compressive force thereto to provide a snapacting over center mechanism whereby a portion of said two relativelywidely spaced stable positions, means responsive to to the attainment ofa predetermined high temperature of said cooking current flowing to saidheating unit, manually actuable means operable on said switch means formanually returning said portion to the other of said two stablepositions, and means including said element for alternately opening andclosing said switch means while said element is in said one of saidpositions to maintain constant the temperature of said cooking device ata temperature below said predetermined high temperature,

10. A temperature control arrangement for an electric heating meanshaving one end fixed and its other end movable in response to changes intemperature, switch means, a resilient member fastened to one of saidmeans, means for applying a compressive silient member to cause said oneof said means position to a secmoves from said first position sition,and means for alternately opening switch means while said element is insaid sectemperature of said cookingdevice for producing relativeseparation of said contacts, and means for manually returning saidelement from said other position to said one position.

12. The control means set forth in claim 11 in which said resilientmeans comprises a closed loop of flat resilient material.

13. Thermal control means fora cooking device of the type including anelectric heating unit and thermal responsive switch with said cookingdevice, said switch means including a resilient element incorporated ina snap acting over center mecha nism whereby said resilient elementassumes two relatively spaced positions, means responsive to a one ofsaid two positions to the other two positions References Cited in thefile of this patent UNITED STATES PATENTS Number Name Date 1,448,240Spencer Mar. 13, 1923 1,743,073 Simmons Jan. 7, 1930 1,809,305 MatthewsJune 9, 1931 2,137,073 Bletz Nov. 15, 1938 2,141,775 Varley Dec. 27,1938 2,262,355 Clark Nov. 11, 1941 2,281,319 Newell Apr. 28, 19422,312,555 Jepson Mar. 2, 1943 2,313,969 Riche Mar. 16, 1943 2,399,406Toth Apr. 30, 1946 2,504,728 Purpura Apr. 18, 1950 2,552,420 Frankel May8, 1951 FOREIGN PATENTS Number Country Date 624,587 Great Britain June13, 1949

